Our present invention relates to a conveyor apparatus for open-cut mining and especially for removal of the overburden and mine deposits in the formation of stopes in a step-like manner with progressively increasing widening of the excavation with increasing excavation depth.
In open-cut mining the overburden and mine deposits are removed in a step-like formation, i.e. with the formation of stopes. The depth of the excavation continuously increases and with increasing depth, there is an increased widening of the funnel-shaped opening of the excavation. The excavator is usually moved along a bottom of the excavation to form a stope and, depending upon the stability of the ground, the equipment used and economic conditions, the stope height can average around 15 m and for the removal of the loose material, the inclined planes between the stopes serve as roads along which the excavated material is removed. The deeper the deposit being mined, the wider must be the opening of the cut by a factor of 400 to 600, thereby defining the funnel shape of the excavation. Material loosened by drilling or explosives (hard rock and solid ores) as well as the overburden are transported away as a rule in trucks formed as trough tippers, mine cars and the like. These trucks travel from the stopes to the grade surface or ground level along the road. The serpentine path increases with mining depth and the travel can be at a speed of about 10 Km/h upwardly and about 35 Km/h downwardly. This requires high concentration of the part of the vehicle drivers and always creates the possibility of accidents.
It is the principal object of the present invention to provide a conveyor apparatus which can carry out mined material including the mined deposit and the overburden from locations in an open-cut mining operation to the surface in a more economical and reliable manner without significant cost.
Another object of the invention is to provide an apparatus for this purpose which allows adjustment to increasing mining depths.
It is also an object of this invention to provide a conveyor apparatus for open-cut mining in a funnel-shaped excavation with removal of overburdened mined deposits, formations of stopes and increased width at an opening of the funnel-shaped excavation at grade level with increased excavation depth, whereby the drawbacks of earlier excavation techniques are avoided, long transport distances are eliminated and the danger of accidents is minimized.
Still another object of this invention is to provide an improved apparatus which obviates the drawbacks of earlier excavation systems.
The objects are attained, in accordance with the invention in a conveyor apparatus for the purposes described and which can be advanced downwardly for increasing depth of excavation. The conveyor apparatus of the invention comprises:
an inclined elevator extending from an edge of the opening at grade level to the floor level;
a traveling platform riding on the inclined elevator and adapted to receive a truck to be filled with overburden or mined deposits;
at least one cable passing over separate upper and lower cable pulleys and having an upper pass of the cable extending to the upper cable pulley from the traveling platform and a lower pass of the cable extending from the lower cable pulley along the elevator;
a counterweight riding on the elevator and connected to the lower pass of the cable; and
a conveyor mechanism operating at grade level at an upper end of the elevator and having a cable drum looped by a portion of the cable between the upper and lower cable pulleys.
According to the invention, therefore, an elevator along which trucks for receiving the mined material can be guided is provided to extend from an edge of the opening of the funnel-shaped excavation at grade level to a floor level at which excavation is carried out and preferably to the bottom of the cut. At least one cable is provided which has upper and lower passes extending over respective cable pulleys with the upper pass of the cable being affixed to a platform on which the car, usually a trough tripper or dumpable car can be carried while the lower pass of the cable is affixed to a counterweight. Both the platform and the upper weight are being guided along the inclined conveyor.
At grade level the cable passes around a conveyor mechanism or machine. The mined material carried by the car or truck is thus transported along the elevator in an upward direction to the edge of the cut.
Because of the inclination of the conveyor which can correspond to the inclination of the funnel-shaped excavation, e.g. even with increasing mining depth, and by elimination of the serpentine path which the cars or truck had to travel previously from the bottom of the excavation to the top thereof, the distance which the trucks travel is minimized thereby simplifying the operations and minimizing the burden placed on the trucks or cars.
A loaded truck or car at the bottom of the excavation need only be placed on the platform in its lowered position, secured in place with appropriate arresting means and then transported driverlessly to the surface at which point another driver can take over control and transport of the car or truck. The result is a highly flexible, economical usage of personnel since different individuals can be provided at the surface and at the floor of the excavation for transport purposes.
Since the counterweight moves in a direction opposite the platform and balances the comparatively high weight of the platform and the loaded car, which may amount to about 500 metric tons, the net mass which must be displaced by the input of energy can be only a fraction of the sum of the load carried by the truck or car, the weight of the truck or car itself, the weight of the platform and the weight of the cable paths connected thereto. The conveyor mechanism thus need only supply a fraction of the energy which would otherwise be necessary to move this latter total mass. It is possible to operate in a single track system with the workload operating in its track and the counterweight in its track.
According to a feature of the invention, the conveyor mechanism driving the cable has a rerouting drum looped by the or each cable and between the upper and lower passes of the or each cable or has individual pulleys or wheels for each cable, the cable returning after being looped around this drum or the rerouting pulleys. The conveyor mechanism or drive may be of the Koepe type.
Preferably the rerouting drum is connected with the conveyor mechanism with a variable spacing therebetween, the system including a cable magazine containing a supply of cable for lengthening of the travel of the cable. With increasing depth of excavation and thus with increasing travel distance, the cable must be effectively lengthened so that there is a progressive increase in the cable weight as well.
For deeper excavations and thus the need to displace the platform to increasingly greater depths, it is merely necessary to release the rerouting drum anchored to the foundation and move it to a new position closer to the drum of the drive mechanism. The movable drum is then fixed at this new position. The rerouting drum can have a diameter of, for example, 9 m and can have journal blocks which are shiftable linearly on respective tracks. The force required for the shifting can be developed hydraulically and when a number of cables are provided for the elevator, a corresponding number of rerouting pulleys can be used instead of a single rerouting drum. For increased output of the mine, a multiplicity of such inclined elevators can be provided in the funnel-shaped excavation in spaced apart relationship therein.
According to a preferred embodiment of the invention, the rerouting drum or assembly of pulleys or rerouting roller can be inclined to the horizontal and each cable can pass around the cable drum of the drive mechanism with double looping so that each cable has at least two turns on the cable drum in a pair of grooves. This permits the drive to be a conventional Koepe conveyor machine because, with the double looping, sufficient friction against the cable drum is achieved to enable the cable system to move extremely large loads which could not be handled by a Koepe drive machine with a single 180xc2x0 looping of the cables. The double looping provides cables in two grooves to prevent slippage under the high weights which must be transported. Alternatively a drum drive machine would have to be very large and hence very expensive to handle lengths of cable which can exceed 700 m, multiple cables of such length, and the loads coupled to them. The inclined orientation of the rerouting roller or the individual pulleys enables the double looping of the or each cable without danger that cross over regions will bring about contact of upper and lower cable passes.
In that connection, the upper pass and lower pass cable pulleys are offset vertically relative to the cable drum of the drive machine. The upper cable stretch and the lower cable stretch pass tangentially onto the rerouting roller and from the latter without interference of the oppositely travelling passes with one another.
According to a further feature of the invention and in another embodiment thereof, to provide a greater degree of looping of the cable around the drum or pulley of the drive mechanism and thus affording increased friction force between the cable and cable carrier to allow large load ratios between the traveling platform cable and the counterweight cable, the upper and lower cable pulleys are laterally offset with respect to the drive machine and preferably offset from one another oppositely. This arrangement can permit a looping of about 240xc2x0 around the cable drum or pulley of the drive. The cable coming from the platform passes over the upper cable pulley and can meet the groove of the cable on the drive machine at a slight angle, e.g. of 0.7 grad.
This deflection is obtained in spite of the fact that the cable pulleys have their axis parallel to the axis of the drive machine and perpendicular to the axis of displacement by laterally offsetting the upper and lower cable pulleys with respect to the center of the cable guide on the drum. After a 240xc2x0 looping in the groove of the cable carrier on the drive machine, the cable is deflected again at an angle of 0.7 grad in the opposite direction to the lower cable pulley and to the latter toward the counterweight. Since the center of the cable of the lower pulley is thus slightly offset from the center of the cable on the drive machine, at the crossing point between the oncoming and outgoing cable a substantial separation can be provided so that the passes do not interfere with one another. The angle or degree of offset thus contributes to the requirement for noninterfering cable travel even in the case of jumping of the cable. All of the cables in all of the regions which are equivalent can be parallel to one another.
The slight oncoming and outgoing angle which would otherwise be required at the cable pulleys can be eliminated in that the cable pulley axes can be inclined to the foundation. The lateral shifting of the cable centers on the one hand between the upper cable disk and the drive and on the other hand between the drive and the lower cable disk can be compensated by connecting the cables to the counterweight asymmetrically with respect to the center of gravity of the latter.
According to a further feature of the invention the cable magazine to compensate for increasing depth by effectively lengthening can be provided on the platform or the counterweight in the form of a windlass drum which is looped by two or more turns of the or each cable. Sufficient friction is thus obtained by the plural looping in that the plural looping has been found to provide a sufficient level of friction. The multiple turns for cable allow sufficient cable to be stored for usual mining operations. With a diameter of the windlass drum of 3 m, cable useful lives of two years with increases in depth of say 15 m per year may require three additional turns per cable. The arrangement of a windlass drum as the cable supply has the advantage that the weight of the windlass drum and the cable supply can be part of the counterweight which would otherwise have to be weighted additionally.
According to a feature of this aspect of the invention, the windlass drum is mounted rotatably on a support frame or has a shaft common to a number of windlass drums mounted don the support frame. If required the requisite cable supply can be provided in readiness and mounted with the support frame or on the support frame. The windlass drums can be driven by a motor via a chain drive although the pay out of an additional cable supply is naturally done in load-free state of the cable.
In a multiple cable arrangement, each windlass drum can be provided with a hydraulic cylinder and locking device which can serve to take up the load and thus relieve the motor and chain transmission from the load when the load is reapplied.
This mechanism can operate following rotation of the drum to pay out (or take up) excess cable or to engage the drum for retensioning of the cable. The hydraulic cylinder and locking device can be mounted on the support frame. The cable, the hydraulic cylinder and the locking mechanism can extend in the force application directly and can relieve the drive of the windlass drum from cable tension forces as has been mentioned.
According to still another feature of the invention, the traveling platform is formed in two parts from a frame and a removable bottom which is seated on this frame. This feature increases the transport reliability since the bipartite configuration enables the bottom with the considerable weight of the loaded truck to be held both in upper and in lower positions for loading and unloading relative to the elevator without lengthening the cables by loading or shortening the cables by unloading. In other words the bottom can be locked to the foundation, according to the invention, independently of the traveling frame in upper and lower positions of bottom and with precision.
For this purpose, at the four corner regions of the bottom, recesses or notches are provided into which upper and lower retaining pawls, controlled by appropriate signals, can be swung. As soon as the platform has been slowed down and shortly before it is brought to standstill, the end position which can be signalled by limit switches or other electrical monitoring means can cause the retaining pawls to be swung into the travel path and swung either above or below the bottom to engage the latter. Further lifting or lowering is then not possible even when, for example, the support frame continues to travel.
According to a further feature of the invention, at the four corners of the bottom there are holes in which pins of the traveling frame engage, the holes and the pins being inclined in the travel direction. At each of the four corners two mechanically independent retaining pawls can be provided which engage over or under the removal bottom and which are free to move only when the friction force of the bottom against the respective pawl is relieved. When the pawls are all swung inwardly and the bottom is pressed against the upper pawls, a signal instructing the pawls to swing outwardly will only be effective on the pawls lower whereas the reverse is true when the weight of the bottom is on the lower pawls. When of course the frictional contact is relieved, the pawls which have been frictionally retained are permitted to swing.